Partitioning of Small Molecules in Hydrogen-Bonding Complex Coacervates of Poly(acrylic acid) and Poly(ethylene glycol) or Pluronic Block Copolymer

Complex coacervation of polymers can be a route to the compartmentalization of aqueous solutions. Presented here is a study of the hydrogen-bonded complex coacervation of poly(acrylic acid) and poly(ethylene glycol) or Pluronic block copolymers and the ability of these coacervates to encapsulate various ionic and nonionic dyes as well as a pharmaceutical compound within them. The formation of complex coacervate driven by hydrogen bonding is studied as a function of both pH and salt content with turbidimetry and isothermal calorimetry. Small-angle X-ray scattering shows the presence of micelles within Pluronic containing coacervate materials formed with a Pluronic block copolymer concentration higher than its critical micelle concentration. Although dyes generally partition to the coacervate phase, in the absence of salt, dyes that are able to hydrogen bond with the coacervate components are better incorporated into the coacervate. It is observed that the addition of salt to the polymer solutions increases the hydrophobicity of the environment within the coacervate, increasing the ability to sequester dye molecules for which there is no hydrogen bonding with the coacervate components. These materials are characterized with UV-vis spectroscopy, dynamic light scattering, zeta potential measurements, isothermal calorimetry, small-angle X-ray scattering, and fluorescence spectroscopy.